Medical devices including aerated adhesive bonds and methods of forming the same

ABSTRACT

Medical devices can be formed from medical device components that are bonded together with an adhesive that resists stresses caused by adhesive curing. In particular, a medical device can include a first component and a second component. The second component can be configured to fit at least partially over the first component. An aerated adhesive layer can be formed or disposed between the first and second components.

TECHNICAL FIELD

The invention relates generally to medical devices and more specificallyto medical devices formed by bonding together medical device components.In particular, the invention relates to medical devices formed bybonding together medical device components using aerated adhesives.

BACKGROUND

A variety of medical devices include multiple components that aresecured together. In particular, some medical devices such as cathetersinclude multiple components such as an elongate shaft and a hub that issecured to the elongate shaft. Some catheters include luer fittings orother fluid-competent connectors that are secured to the elongate shaft.In some catheters, multiple segments can be joined together to form theelongate shaft. In some catheters, a strain relief is positionedintermediate the hub and the elongate shaft and is secured to bothelements.

Medical device components can be secured together using a variety oftechniques, including mechanical connections and chemical joiningtechniques such as adhesives and, in particular, light-cured adhesives.However, light-cured adhesives can exhibit shrinkage upon curing. As theadhesive reduces in volume while curing, stresses can build within theadhesive layer. These stresses can, in some instances, result indelamination between the adhesive layer and each of the components incontact with the adhesive layer.

One solution to this issue is to limit the maximum thickness of theadhesive layer by limiting the gap between the surfaces to be adhesivelysecured. While this technique can reduce issues with delamination andother adhesive failures, it can place additional demands on thetolerances to which each of the components must be manufactured.

A need remains, therefore, for an improved method of securing medicaldevice components together. A need remains for improved adhesivetechniques in forming medical devices.

SUMMARY

The invention is directed to medical devices that are formed frommedical device components that are bonded together with an adhesive thatresists stresses caused by adhesive curing.

Accordingly, an example embodiment of the invention can be found in amedical device that includes a first component and a second component.The first component has an outer surface that includes an outerengagement portion and the second component has an inner surface thatincludes an inner engagement portion. The inner engagement portion isconfigured to fit over the outer engagement portion. An aerated adhesivelayer is positioned between the inner engagement portion and the outerengagement portion.

Another example embodiment of the invention can be found in a method offorming a medical device that has a first component with an outersurface and a second component with an inner surface. An aeratedadhesive layer is disposed over at least a portion of the outer surfaceof the first component. The second component is disposed over the firstcomponent such that at least a portion of the inner surface contacts theaerated adhesive layer, and the aerated adhesive layer is cured.

Another example embodiment of the invention can be found in a method offorming a medical device that has a first component with an outersurface and a second component with an inner surface. The secondcomponent is disposed over the first component such that at least aportion of the inner surface thereof is proximate at least a portion ofthe outer surface of the first component. An aerated adhesive isinjected between the outer surface of the first component and the innersurface of the second component to form an aerated adhesive layer, andthe aerated adhesive layer is subsequently cured.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a plan view of an intravascular catheter in accordance with anembodiment of the invention;

FIG. 2 is a cross-sectional view of the intravascular catheter of FIG.1, taken along the 2-2 line;

FIG. 3 is a partially-sectioned view of a medical device in accordancewith an embodiment of the invention;

FIG. 4 is a cross-sectional view of the medical device of FIG. 3, takenalong the 4-4 line;

FIG. 5 is a cross-sectional view of the medical device of FIG. 4, takenalong the 5-5 line;

FIG. 6 is a partially-sectioned view of a medical device in accordancewith an embodiment of the invention;

FIG. 7 is a partially-sectioned view of a medical device in accordancewith an embodiment of the invention; and

FIG. 8 is a partially-sectioned view of a medical device in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

All numeric values are herein assumed to be modified by the term“about”, whether or not explicitly indicated. The term “about” generallyrefers to a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the terms “about” may include numbers thatare rounded to the nearest significant figure.

The recitation of numerical ranges by endpoints includes all numberswithin that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4,and 5).

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. As used in this specification and theappended claims, the term “or” is generally employed in its senseincluding “and/or” unless the content clearly dictates otherwise.

The following description should be read with reference to the drawingswherein like reference numerals indicate like elements throughout theseveral views. The drawings, which are not necessarily to scale, depictillustrative embodiments of the claimed invention.

FIG. 1 is a plan view of a catheter 10 that can be assembled inaccordance with an embodiment of the invention. The catheter 10 can beone of a variety of different catheters, but is preferably anintravascular catheter. Examples of intravascular catheters includeballoon catheters, atherectomy catheters, drug delivery catheters,diagnostic catheters and guide catheters. Except as described herein,the intravascular catheter 10 can be manufactured using conventionaltechniques and materials.

The intravascular catheter 10 can be sized in accordance with itsintended use. The catheter 10 can have a length that is in the range ofabout 50 centimeters to about 140 centimeters and can have a diameterthat is in the range of about 3 F (French) to about 9 F.

In the illustrated embodiment, the intravascular catheter 10 includes anelongate shaft 12 that has a proximal region 14, a distal region 16 anda distal end 18. A hub and strain relief assembly 20 can be connected tothe proximal region 14 of the elongate shaft 12. The hub and strainrelief assembly 20 includes a main body portion 22, a pair of flanges 24designed to improve gripping, and a strain relief 26 that is intended toreduce kinking. The hub and strain relief assembly 20 can be ofconventional design and can be attached using conventional techniques.

FIG. 2 is a cross-sectional view of the elongate shaft 12, taken alongline 2-2 of FIG. 1. The elongate shaft 12 includes an outer layer 28 andan inner layer 30. Each of the outer layer 28 and the inner layer 30 canextend from the proximal region 14 of the elongate shaft 12 to thedistal region 16 of the elongate shaft 12. The inner layer 30 defines alumen 32 that extends through the elongate shaft 12.

In some embodiments, as illustrated, the elongate shaft 12 can include areinforcing braid or ribbon layer 34 to increase particular propertiessuch as kink resistance. A reinforcing braid or ribbon layer 34 can bepositioned between the outer layer 28 and the inner layer 30. Thereinforcing braid or ribbon layer can be provided in a configurationthat provides adequate kink resistance without substantially increasingthe overall profile of the elongate shaft 12.

In some embodiments (not specifically illustrated), the elongate shaft12 can include one or more shaft segments having varying degrees offlexibility. For example, the elongate shaft 12 can include a proximalsegment, an intermediate segment and a distal segment. In someembodiments, the elongate shaft 12 can also include a distal tip segmentthat can be formed from a softer, more flexible polymer. The elongateshaft 12 can include more than three segments, or the elongate shaft 12can include fewer than three segments.

If the elongate shaft 12 has, for example, three segments such as aproximal segment, an intermediate segment and a distal segment, eachsegment can include an inner layer 30 that is the same for each segmentand an outer layer that becomes increasingly more flexible withproximity to the distal end 18 of the elongate shaft 12. For example,the proximal segment can have an outer layer that is formed from apolymer having a hardness of 72 D (Durometer), the intermediate segmentcan have an outer layer that is formed from a polymer having a hardnessof 68 D and the distal segment can be formed from a polymer having ahardness of 46 D.

If the elongate shaft 12 has three segments, each of the segments can besized in accordance with the intended function of the resulting catheter10. For example, the proximal segment can have a length of about 35inches, the intermediate segment can have a length that is in the rangeof about 2 inches to about 3 inches, and the distal segment can have alength that is in the range of about 1 inch to about 1.25 inches.

The inner layer 30 can be a uniform material and can define a lumen 32that can run the entire length of the elongate shaft 12 and that is influid communication with a lumen (not illustrated) extending through thehub assembly 20. The lumen 32 defined by the inner layer 30 can providepassage to a variety of different medical devices, and thus the innerlayer 30 can include, be formed from or coated with a lubriciousmaterial to reduce friction within the lumen 32. An exemplary materialis polytetrafluoroethylene (PTFE), better known as TEFLON®. The innerlayer 30 can be dimensioned to define a lumen 32 having an appropriateinner diameter to accommodate its intended use. In some embodiments, theinner layer 30 can define a lumen 32 having a diameter of about 0.058inches and the inner layer 30 can have a wall thickness of about 0.001inches.

The outer layer 28 can be formed from any suitable polymer that willprovide the desired strength, flexibility or other desiredcharacteristics. Polymers with low durometer or hardness can provideincreased flexibility, while polymers with high durometer or hardnesscan provide increased stiffness. In some embodiments, the polymermaterial used is a thermoplastic polymer material. Some examples of somesuitable materials include polyurethane, elastomeric polyamides, blockpolyamide/ethers (such as PEBAX®), silicones, and co-polymers. The outerlayer 28 can be a single polymer, multiple layers, or a blend ofpolymers. By employing careful selection of materials and processingtechniques, thermoplastic, solvent soluble, and thermosetting variantsof these materials can be employed to achieve the desired results.

In particular embodiments, a thermoplastic polymer such as aco-polyester thermoplastic elastomer such as that available commerciallyunder the ARNITEL® name can be used. The outer layer 28 can have aninner diameter that is about equal to the outer diameter of the innerlayer 30.

In some embodiments, the outer layer 28 can have an inner diameter inthe range of about 0.060 inches to about 0.070 inches and an outerdiameter in the range of about 0.064 inches to about 0.078 inches. Partor all of the outer layer 28 can include materials added to increase theradiopacity of the outer layer 28, such as 50% bismuth subcarbonate.

FIGS. 3 through 8 illustrate medical devices formed by adhesivelysecuring two components together using an aerated adhesive in accordancewith embodiments of the present invention. The first and secondcomponents can generically represent any two medical device componentsthat can be adhesively secured together. In some embodiments, the firstand second components can individually represent, respectively, anelongate shaft 12 and a hub assembly 20 (see FIG. 1). In someembodiments, the first and second components can represent an elongateshaft 12 and a strain relief 26 (see FIG. 1). In some embodiments, thefirst and second components can represent a strain relief 26 and a hubassembly 20 (see FIG. 1).

In particular, FIGS. 3 through 5 illustrate an assembly 36 that includesa first component 38 and a second component 40. The first component 38has an outer surface 42 that in part defines an outer engagement portion44. Similarly, the second component 40 has an inner surface 46 that inpart defines an inner engagement portion 48. The first component 38defines a lumen 50. FIG. 4 is a cross-sectional view through theassembly 36 proximate the outer and inner engagement portions 44 and 48.

Each of the first component 38 and the second component 40 can be formedof any suitable material such as a polymeric material and can be formedto any suitable dimension, as discussed above with respect to FIGS. 1and 2. As illustrated, each of the first component 38 and the secondcomponent 40 are cylindrical in shape, but in other embodiments,additional structures and shapes are contemplated.

In some embodiments, the first component 38 can have an overall lengththat is in the range of about 50 cm to about 140 cm, an inner diameterthat is in the range of about 2 F to about 8 F and an outer diameterthat is in the range of about 3 F to about 9 F. In some embodiments, thesecond component 40 can have an overall length that is in the range ofabout 1 inch to about 3 inches, an inner diameter that is in the rangeof about 3 F to about 10 F and an outer diameter that is in the range ofabout 4 F to about 11 F.

In the illustrated embodiment, the outer engagement portion 44 of thefirst component 38 has an outer diameter that is at least substantiallythe same as an outer diameter of the first component 38 beyond the outerengagement portion 44. The outer engagement portion 44 can have a lengththat is in the range of about 0.020 inch to about 0.500 inch. Similarly,the inner engagement portion 48 of the second component 40 has an innerdiameter that is at least substantially the same as an inner diameter ofthe second component 40 beyond the inner engagement portion 48. Theinner engagement portion 48 can have a length that is in the range ofabout 0.020 inch to about 0.500 inch.

In other embodiments, as will be discussed in greater detailhereinafter, the outer engagement portion 44 can have a decreased outerdiameter. In other embodiments, the second component 40 can beconfigured to fit within the first component 40, and in this instance,the outer engagement portion 44 can have an increased diameter.

An aerated adhesive layer 52 is positioned between the outer engagementportion 44 and the inner engagement portion 48. The distance between theouter engagement portion 44 and the inner engagement portion 48 canvary, depending on the tolerances to which each of the first component38 and the second component 40 are manufactured. In some embodiments,the distance between the outer engagement portion 44 and the innerengagement portion 48 can vary from about 0.001 inch to about 0.010inch.

Therefore, in some embodiments, the aerated adhesive layer 52 can varyin thickness from about 0.001 inch to about 0.010 inch, and can have anaverage thickness that is in the range of about 0.002 inch to about0.008 inch. In some embodiments, the assembly 36 can be formed bydisposing an aerated adhesive over the outer engagement portion 44 ofthe first component 38, followed by disposing the inner engagementportion 48 of the second component 40 over the outer engagement portion44.

In other embodiments, the assembly 36 can be formed by disposing thesecond component 40 over the first component 38 such that the innerengagement portion 48 overlies the outer engagement portion 44. Anaerated adhesive can subsequently be injected into a void between theouter and inner engagement portions 44 and 48. The aerated adhesive cansubsequently be cured to form the aerated adhesive layer 52.

In some embodiments, it can be advantageous to put together the assembly36 under an inert atmosphere. Any suitable inert gas can be used, eitherat atmospheric pressure or at above-atmospheric pressure, but argon andnitrogen are preferred. In particular embodiments, the assembly 36 canbe formed under a nitrogen gas atmosphere at a pressure that is in therange of about 2 psig to about 15 psig.

FIG. 5 is an axial cross-section taken through FIG. 4, betterillustrating the aerated adhesive layer 52. The aerated adhesive layer52 can include any suitable adhesive material. In particular, theaerated adhesive layer 52 can be formed from any suitable light-curableadhesive. Suitable examples include acrylic, epoxy, acrylic/epoxy, andacrylic/urethane based adhesives.

The aerated adhesive layer 52 includes a plurality of voids 54 that canbe formed in a variety of ways. In some embodiments, the voids 54 can beformed by metering an inert gas into the adhesive stream while applyingthe adhesive to the surfaces to be joined.

Other methods of forming the voids 54 include metering the adhesive andinert gas through a mixing tube.

In some embodiments, the voids 54 can include an inert gas at ambient orabove-ambient pressure. In particular embodiments, the voids 54 containnitrogen gas at a pressure that is in the range of about 2 psig to about15 psig.

The voids 54 can provide distensible regions within the aerated adhesivelayer 52 that can distend or deform in response to stresses caused bythe adhesive shrinking while curing. The voids 54 can vary in size, butin some embodiments the voids 54 can have an average diameter of about0.001 inch. In some embodiments, the aerated adhesive layer 52 caninclude an amount of voids 54 that is in the range of about 25 to about50 volume percent. The aerated adhesive layer 52 can have a density thatis reduced by about 25 to about 50 percent with respect to a density ofthe adhesive itself without any aeration.

In some embodiments, it maybe useful for a completed assembly to have aconstant outer diameter. FIG. 6 shows an assembly 55 having a constantouter diameter. The assembly 55 includes a first component 56 and asecond component 58 that can be formed of any suitable material and toany suitable dimension, as discussed previously with respect to FIG. 3.The first component 56 has an outer surface 60 that in part defines anouter engagement portion 62. The second component 58 has an innersurface 64 that in part defines an inner engagement portion 66. Anaerated adhesive layer 68 is disposed between the outer engagementportion 62 and the inner engagement portion 66.

As illustrated, the outer engagement portion 62 of the first component56 has an outer diameter that is reduced with respect to an outerdiameter of the first component beyond the outer engagement portion 62.In some embodiments, the outer engagement portion 62 can have an outerdiameter that is reduced an amount substantially equal to the thicknessof the inner engagement portion 66 of the second component 58 plus thethickness of the aerated adhesive layer 68. In some embodiments, theouter engagement portion 62 can have an outer diameter that is reducedabout 35 to about 65 percent.

While not illustrated, in some embodiments, the outer engagement portion62 can have an outer diameter that is reduced somewhat with respect toan outer diameter of the first component 56 beyond the outer engagementportion 62, and the inner engagement portion 66 can have an innerdiameter that is increased somewhat with respect to an inner diameter ofthe second component 58 beyond the outer engagement portion 66.

In other embodiments, it may be useful for a completed assembly to havea lumen having at least a substantially constant diameter. FIG. 7illustrates an assembly 70 that includes a first component 72 and asecond component 74 that can be formed of any suitable material and toany suitable dimension, as discussed previously with respect to FIG. 3.The first component 72 has an outer surface 76 that in part defines anouter engagement portion 78. The second component 74 has an innersurface 80 that in part defines an inner engagement portion 82. Anaerated adhesive layer 84 is disposed between the outer engagementportion 78 and the inner engagement portion 82.

The inner engagement portion 82 can have an inner diameter that isincreased with respect to an inner diameter of the second component 74beyond the inner engagement portion 82. In some embodiments, the innerengagement portion 82 can have an inner diameter that is sufficientlyincreased to accommodate a wall thickness of the outer engagementportion 78 and a thickness of the aerated adhesive layer 84. As aresult, a lumen 86 extending through the assembly 70 can have at least asubstantially constant diameter.

In some embodiments, several components can be secured together. FIG. 8illustrates an assembly 88 that includes a first component 90, a secondcomponent 92 and a third component 94 that can be formed of any suitablematerial and to any suitable dimension, as discussed previously withrespect to FIGS. 1-3. In some embodiments, the first component 90 canrepresent an elongate shaft, the second component 92 can represent astrain relief and the third component 94 can represent a hub or otherconnector.

In some embodiments, the first component 90 can have an overall lengththat is in the range of about 50 cm to about 140 cm, an inner diameterthat is in the range of about 2 F to about 8 F and an outer diameterthat is in the range of about 3 F to about 9 F. In some embodiments, thesecond component 92 can have an overall length that is in the range ofabout 1 inch to about 3 inches, an inner diameter that is in the rangeof about 3 F to about 10 F and an outer diameter that is in the range ofabout 4 F to about 11 F. In some embodiments, the third component 94 canhave an overall length that is in the range of about 1 inch to about 2inches, and an inner diameter that is in the range of about 3 F to about11 F.

The first component 90 can have an outer surface 96 that in part definesan outer engagement portion 98. The second component 92 can have aninner surface 100 that defines in part an inner engagement portion 102and can also have an outer surface 104 that defines in part an outerengagement portion 106. The third component 94 can have an inner surface108 that in part defines an inner engagement portion 110. A lumen 112can extend through the assembly 88.

A first aerated adhesive layer 114 can be disposed between the outerengagement portion 98 of the first component 90 and the inner engagementportion 102 of the second component 92. A second aerated adhesive layer116 can be disposed between the outer engagement portion 106 of thesecond component 92 and the inner engagement portion 110 of the thirdcomponent 94. In some embodiments, the first aerated adhesive layer 114and the second aerated adhesive layer 116 can be separately formed,possibly of different aerated adhesives. In some embodiments, the firstaerated adhesive layer 114 and the second aerated adhesive layer 116 canrepresent a single continuous aerated adhesive layer.

Medical devices as described herein can be partially or completelycoated with a lubricious or other type of coating. Hydrophobic coatingssuch as fluoropolymers provide a dry lubricity that can improve handlingand device exchanges. An example of a suitable fluoropolymer ispolytetrafluoroethylene (PTFE), better known as TEFLON®.

Lubricious coatings can improve steerability and improve lesion crossingcapability. Examples of suitable lubricious polymers include hydrophilicpolymers such as polyarylene oxides, polyvinylpyrolidones,polyvinylalcohols, hydroxy alkyl cellulosics, algins, saccharides,caprolactones, and the like, and mixtures and combinations thereof.Hydrophilic polymers can be blended among themselves or with formulatedamounts of water insoluble compounds (including some polymers) to yieldcoatings with suitable lubricity, bonding, and solubility. In someembodiments, a distal portion of a composite medical device can becoated with a hydrophilic polymer as discussed above, while the moreproximal portions can be coated with a fluoropolymer.

The medical devices described herein can include, or be doped with,radiopaque material to improve visibility when using imaging techniquessuch as fluoroscopy techniques. Any suitable radiopaque material knownin the art can be used. Some examples include precious metals, tungsten,barium subcarbonate powder, and the like, and mixtures thereof. In someembodiments, radiopaque material can be dispersed within the polymersused to form the particular medical device. In some embodiments, theradiopaque materials distinct from the ferromagnetic materials aredispersed.

It should be understood that this disclosure is, in many respects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size, and arrangement of steps without exceeding the scope of theinvention. The invention's scope is, of course, defined in the languagein which the appended claims are expressed.

1. A medical device, comprising: a first component having an outer surface including an outer engagement portion; a second component having an inner surface including an inner engagement portion, the inner engagement portion configured to fit over the outer engagement portion; and an aerated adhesive layer positioned between the inner engagement portion and the outer engagement portion.
 2. The medical device of claim 1, wherein the aerated adhesive layer resists delamination between the aerated adhesive layer, the inner engagement portion and the outer engagement portion.
 3. The medical device of claim 1, wherein the aerated adhesive layer absorbs stresses resulting from curing of the aerated adhesive.
 4. The medical device of claim 1, wherein the aerated adhesive layer comprises distensible regions.
 5. The medical device of claim 1, wherein the aerated adhesive layer comprises a light-curable adhesive.
 6. The medical device of claim 5, wherein the light-curable adhesive comprises an adhesive selected from the group consisting of acrylic, epoxy, acrylic/epoxy, and acrylic/urethane based adhesives.
 7. The medical device of claim 1, wherein the aerated adhesive layer comprises a plurality of voids.
 8. The medical device of claim 7, wherein the plurality of voids comprise at least about 25 percent volume of the aerated adhesive layer.
 9. The medical device of claim 7, wherein the voids include an inert gas.
 10. The medical device of claim 9, wherein the inert gas comprises N₂.
 11. The medical device of claim 9, wherein the inert gas is at ambient pressure.
 12. The medical device of claim 9, wherein the inert gas is at greater than ambient pressure.
 13. The medical device of claim 1, wherein the aerated adhesive layer has an effective density that is about 25 to about 50 percent less than a density of the adhesive material itself.
 14. The medical device of claim 1, wherein a gap between the outer surface of the first component and the inner surface of the second component is at least about 0.001 inch.
 15. The medical device of claim 1, wherein the aerated adhesive layer has an average thickness that is in the range of about 0.002 inch to about 0.008 inch.
 16. The medical device of claim 1, wherein the first component comprises an elongate shaft and the second component comprises a hub.
 17. The medical device of claim 1, wherein the first component comprises an elongate shaft and the second component comprises a strain relief.
 18. The medical device of claim 1, wherein the first component comprises a strain relief and the second component comprises a hub.
 19. A method of forming a medical device comprising a first component having an outer surface and a second component having an inner surface, the method comprising steps of: disposing an aerated adhesive layer over at least a portion of the outer surface; disposing the second component over the first component such that at least a portion of the inner surface contacts the aerated adhesive layer; and curing the aerated adhesive layer.
 20. The method of claim 19, wherein the aerated adhesive comprises an adhesive selected from the group consisting of acrylic, epoxy, acrylic/epoxy, and acrylic/urethane based adhesives, with a plurality of voids dispersed within the adhesive.
 21. The method of claim 20, wherein the plurality of voids comprise at least about 25 percent volume of the aerated adhesive layer.
 22. The method of claim 20, wherein the method is carried out under an inert atmosphere.
 23. The method of claim 22, wherein the inert atmosphere comprises nitrogen and is at a pressure greater than ambient atmospheric pressure.
 24. The method of claim 19, wherein the aerated adhesive layer has an effective density that is about 25 to about 50 percent less than a density of the adhesive material itself.
 25. The method of claim 19, wherein disposing the second component over the first component results in a gap therebetween that is at least about 0.001 inch.
 26. The method of claim 19, wherein the first component comprises an elongate shaft and the second component comprises a hub.
 27. The method of claim 19, wherein the first component comprises an elongate shaft and the second component comprises a strain relief.
 28. The method of claim 19, wherein the first component comprises a strain relief and the second component comprises a hub.
 29. A method of forming a medical device comprising a first component having an outer surface and a second component having an inner surface, the method comprising steps of: disposing the second component over the first component such that at least a portion of the inner surface of the second component is proximate at least a portion of the outer surface of the first component; injecting an aerated adhesive between the outer surface of the first component and the inner surface of the second component to form an aerated adhesive layer; and curing the aerated adhesive layer.
 30. The method of claim 29, wherein the aerated adhesive comprises an adhesive selected from the group consisting of acrylic, epoxy, acrylic/epoxy, and acrylic/urethane based adhesives, with a plurality of voids dispersed within the adhesive.
 31. The method of claim 30, wherein the plurality of voids comprise at least about 25 percent volume of the aerated adhesive layer.
 32. The method of claim 30, wherein the method is carried out under an inert atmosphere.
 33. The method of claim 32, wherein the inert atmosphere comprises nitrogen and is at a pressure greater than ambient atmospheric pressure.
 34. The method of claim 29, wherein the aerated adhesive layer has an effective density that is about 25 to about 50 percent less than a density of the adhesive material itself.
 35. The method of claim 29, wherein disposing the second component over the first component results in a gap therebetween that is at least about 0.001 inch.
 36. The method of claim 29, wherein the first component comprises an elongate shaft and the second component comprises a hub.
 37. The method of claim 29, wherein the first component comprises an elongate shaft and the second component comprises a strain relief.
 38. The method of claim 29, wherein the first component comprises a strain relief and the second component comprises a hub. 